It seems to me like an exercise in futility (with all due respect). It has too many parameters projected over a very long time (I mean if you are going to cons

It seems to me like an exercise in futility (with all due respect). It has too many parameters projected over a very long time (I mean if you are going to consider buying a house it means that you are planning some stability over a long stretch of time, like 20 years or more, and anyway very few people can afford to buy a house with a shorter than 20 years mortgage covering 50%-60% or more of the price). You are asked to project for (as said at least 20 years) the inflation rate, the appreciation of the house value, the increase in rents, the investment return rate. While the first three can - maybe - be roughly hypothized (in a "stable" country with a "stable" economy), the latter is highly variable, you may also lose money in investment, or as well you could have an unpredictable very high growth rate. The much simpler rule of thumb of 3% of house value is much faster (still in the 20+ years duration hypothesis). If you can pay for rent less than 3% of current value of the house, then rent, otherwise (if you can afford it) buy.